1. Field of Invention
This invention relates to a focal plane shutter for cameras and to a digital camera provided with the same.
2. Description of the Related Art
Focal plane shutters for digital cameras include focal plane shutters each of which is provided with two kinds of shutter blades called a first blade and a second blade respectively. This type of focal plane shutter has had substantially the same structure as focal plane shutters for film-based cameras do, formerly. A first blade-driving mechanism for focal plane shutters of this type is composed of a first blade-driving member and a first blade-driving spring, and a second blade-driving mechanism for focal plane shutters of this type is comprised of a second blade-driving member and a second blade-driving spring. A first blade and a second blade are connected directly to the first blade-driving member and the second blade-driving member, respectively. In shooting, these two blade-driving members are rotated by the elastic forces of the first blade-driving and second blade-driving springs respectively, in turn. And, the first blade opens an exposure aperture and then the second blade closes the exposure aperture afterward, so that the light-receiving plane of an image sensor like CCD is exposed.
And, when the exposure operations of the first and second blades are complete, imaging information is transferred from the image sensor to a storage device through an information-processing circuit while the second blade is covering the exposure aperture. Afterward, the cocking operation of focal plane shutter of this type is immediately performed in such a way that a cocking member rotated from its initial position makes these two blade-driving members reverse up to their cocked positions against the elastic forces of the respective blade-driving springs. As a result, in a focal plane shutter of this type, the second blade leaves the exposure aperture and the first blade covers the exposure aperture in a state in which the cocking operation is complete, or a state in which the focal plane shutter of this type is on standby for shooting.
Also, mechanisms for preventing the two blade-driving members from rotating until an exposure operation is performed in next shooting include mechanisms called “locking type” and mechanisms called “direct type”. In these two types of mechanism, the locking-type mechanisms are formed in such a way that blade-driving members are made to engage with locking members respectively to be locked in respective their cocked positions. As a result, the cocking member may be made to immediately return to its initial position when the cocking operation is complete, or the cocking member may be made to return to its initial position before the exposure aperture-opening operation of the first blade in releasing camera shutter. And, the respective locking members are operated by respective electromagnets and the respective blade-driving members are released from the respective engagements with the locking members in turn, so that the exposure operations of the first and second blades are performed.
On the other hand, the direct-type mechanisms are formed in such a way that: each of the two blade-driving members is provided with a iron piece member; and the cocking member rotates these blade-driving members, until these iron piece members come into contact with electromagnets not magnetized respectively as a result of the cocking operation. As a result, in the direct-type focal plane shutters, the cocking member does not return to its initial position even after the iron piece members come into contact with the electromagnets not magnetized respectively, so that the cocking member keeps the iron piece members coming into contact with the electromagnets not magnetized. And, when a release button of a camera is pressed in next shooting and each of the electromagnets are magnetized to attract and hold the iron piece members, the cocking member is made to return to its initial position. And, afterward, each of the electromagnets is demagnetized to release the respective iron piece members from the magnetic attractions due to the electromagnets in turn, so that the exposure operations of the first and second blades are performed.
As described above, this type of focal plane shutter is formed in such a way that the exposure aperture is closed by the first blade in a state in which this type of focal plane shutter is on standby for shooting, both in the case of locking-type focal plane shutters and in the case of direct-type focal plane shutters. Accordingly, digital cameras provided with this type of focal plane shutter are usually provided with optical finders, respectively.
Now, there has occurred the necessity that digital cameras provided with focal plane shutter should also include electronic view finders with a crystal liquid display device or the like respectively, as well as digital cameras provided with lens shutter, in recent years. Accordingly, while the number of cameras each of which is provided with only an optical finder as before has decreased, the number of cameras each of which is provided with both of an optical finder and an electronic view finder or provided with only an electronic view finder has increased. And, although there is a publically-known manner in which a camera is provided with an another image sensor for an electronic view finder other than an image sensor for shooting in the case where the camera is provided with the electronic view finder, it is usual to use a single image sensor both for displaying an image and for capturing an image.
However, in the case where a single image sensor is used both for displaying an image and for capturing an image, a focal plane shutter in such a case has to be formed in such a way that: not only a second blade, but also a first blade is made to leave an exposure aperture, in the cocked state of the focal plane shutter; and, when a release button is pressed in shooting, the first blade is operated to cover the exposure aperture at its initial stage, and the exposure aperture is opened by the first blade and by the second blade in turn at the next stage. That is to say, the focal plane shutter in such a case has to be formed in such a way that, in the cocking operation, while the second blade is made to operate from a state of the second blade closing the exposure aperture to a state of the second blade opening the exposure aperture, the first blade is made not to operate from a state of the first blade opening the exposure aperture to a state of the first blade closing the exposure aperture.
In order to achieve such operations of the first and second blades, a focal plane shutter is formed in such a way that: the first blade-driving mechanism is composed of two members which are a first blade-driving first member directly connected to the first blade and a first blade-driving second member directly biased by the first blade-driving spring; in the cocking operation, only the first blade-driving second member is moved to its cocked position so that the first blade keeps opening the exposure aperture to make it possible to observe an object with the electronic view finder; when a release button is pressed in shooting, the cocking member is returned from its cocked position to its initial position at its initial stage, the first blade-driving first member is rotated by the elastic force of a spring weaker than the first blade-driving spring in the process of the return of the cocking member to its initial position (where the spring weaker than the first blade-driving spring is called “first blade-cocking spring” below), so that first blade is moved to close the exposure aperture; and, at the next stage, the first blade-driving second member makes the first blade perform its exposure operation while the first blade-driving second member is being accompanied by the first blade-driving first member, and then the second blade-driving member subsequently makes the second blade perform its exposure operation. Japanese Patent TOKUKAI No. 2001-222059 discloses such a focal plane shutter.
However, the focal plane shutter disclosed in Japanese Patent TOKUKAI No. 2001-222059 is formed in such a way that, when a release button is pressed in shooting and then the cocking member returns to its initial position at the initial stage, the first blade-driving first member is moved just before the return of the cocking member to its initial position is complete, so that the first blade closes the exposure aperture. And, in this case, the first blade-driving first member is rotated from a state of the first blade completely opening the exposure aperture to a state of the first blade completely closing the exposure aperture by the elastic force of the first blade-cocking spring, in one sitting. Accordingly, if any countermeasures are not taken, the first blade bounces large when the operation of the first blade closing the exposure aperture is complete, so that the exposure operation is not allowed to start until the bounce of the first blade stops. Japanese Patent TOKUKAI No. 2003-222928 discloses a focal plane shutter formed in such a way that, when the cocking member returns from its cocked position to its initial position, the first blade-driving first member is moved at the initial stage of the operation of the cocking member returning to its initial position so that the first blade is made to start to close the exposure aperture early.
However, although Japanese Patent TOKUKAI No. 2003-222928 discloses a structure for making it possible to rotate the first blade-driving first member at the stage where the cocking member returns to its initial position when a release button is pressed in shooting, the structure for the focal plane shutter disclosed in Japanese Patent TOKUKAI No. 2003-222928 is not necessarily favorable for mass-producing focal plane shutters. Now, Japanese Patent TOKUKAI No. 2007-298544 discloses a focal plane shutter formed in such a way that: in the process of returning the cocking member to its initial position, the first blade-driving first member is indirectly made to follow the return operation of the cocking member from the beginning of the process so as to make the first blade close the exposure aperture; and the first blade-driving first member is made to stop following the return operation of the cocking member before the cocking member completely returns to its initial position, so that the bounce of the first blade is small and the first blade favorably is stopped when the cocking member stops in its initial position. The focal plane shutter disclosed in Japanese Patent TOKUKAI No. 2007-298544 has a structure extremely favorable also for mass-production.
The present invention relates to improvements in a focal plane shutter for cameras as disclosed in Japanese Patent TOKUKAI No. 2001-222059, Japanese Patent TOKUKAI No. 2003-222928, or Japanese Patent TOKUKAI No. 2007-298544 and in a digital camera provided with the same, the focal plane shutter for cameras being applicable for both the cases of locking type and of direct type and being formed in such a way that: a first blade-driving mechanism includes a first blade-driving first member connected to a first blade and rotated by the elastic force of a first blade-cocking spring until the first blade reaches to its exposure operation-starting position at the initial stage after releasing shutter, and a first blade-driving second member rotated by the elastic force of a first blade-driving spring in the exposure operation and rotating the first blade-driving first member against the elastic force of the first blade-cocking spring so as to make a first blade open an exposure aperture; a second blade-driving mechanism includes a second blade-driving member connected to a second blade and rotated by the elastic force of a second blade-driving spring in the exposure operation so as to make the second blade close the exposure aperture; and, while the first blade-driving second member and the second blade-driving member are made to move to their cocked positions against the driving forces for these blade-driving springs respectively when the cocking member moves from its initial position to its cocked position, the first blade-driving first member is moved to its exposure operation-starting position in the process of returning the cocking member to its initial position after releasing shutter.